(1) Field of the Invention
The invention relates to a method of planarizing an integrated circuit device, and more particularly, to a method of planarizing a submicron integrated circuit device which avoids spin-on-glass non-uniformity defects.
(2) Description of the Prior Art
As devices shrink to the submicron level, interconnects between these devices become finer. Planarized dielectric film must be formed between the metal layers of an integrated circuit in order to achieve good metallization step coverage of the fine interconnects. Spin-on-glass has been used widely for the dielectric film after its curing to silicon oxide. The material to be applied is thoroughly mixed in a suitable solvent. The spin-on-glass material suspended in the vehicle or solvent is deposited onto the semiconductor wafer surface and uniformly spread thereover by the action of spinning the wafer. The material fills the indentations in the integrated circuit wafer surface, that is planarization. Most of the vehicle or solvent is driven off by a low temperature baking step often followed by vacuum degassing. Other coatings of the spin-on-glass material may be applied, baked and vacuum degassed until the desired spin-on-glass thickness layer is formed. The final step in the making of the spin-on-glass layer is curing. Curing is a high temperature heating step to cause the breakdown of the spin-on-glass material to a silicon dioxide like cross linked material.
Serious non-uniformity defects can be inspected after the second coating of the spin-on-glass material if the first coating was not cured prior to the application of the second coating. The non-uniformity appears especially on bond pads, guard rings, and thin metal lines. The root cause of the non-uniformity is that the first coated film reacts insufficiently with the surface of the underlayer, usually a plasma-enhanced silicon oxide. There are two possible solutions to the non-uniformity problem. The first solution is to cure the first spin-on-glass layer before the second layer is applied, and then to cure the second layer after it is deposited. The drawbacks of this solution are that it is too costly and time consuming. The second solution is completely unexpected and is the subject of the present invention. The solution is to apply the spin-on-glass material under a low relative humidity process.